Juvenile onset diabetes involves a loss in pancreatic beta cell function. The process of beta cell development and the regulation of insulin synthesis in the pathogenesis of this disease are not well understood. This proposal is addressed to the study of endocrine pancreatic beta cell development. The experiment to be performed involve the use of purified nucleic acid probes to study gene expression. A purified mRNA can be transcribed by reverse transcriptase to prepare a radioactive complementary DNA (cDNA) copy. This cDNA probe can be used in nucleic acid hybridization experiments allowing quantitative measurements of the specific mRNA concentration and determination of the number genes coding for proinsulin. The first requirement of this research is to identify and purify the messenger RNA for proinsulin. This work is presently in progress in our laboratory; it appears that fetal bovine pancreas is a suitable tissue source for the purification of this RNA species. Successful purification and synthesis of proinsulin cDNA will permit experiments to answer the following questions about beta cell function: (a) Is beta cell maturation accompanied by the transcriptional regulation of proinsulin biosynthesis? (b) How many sequences (genes) complementary to pro-insulin cDNA are in the human and bovine genomes?